Scintillation detectors are used to measure and assess multiple types of ionizing radiation which includes alpha-, beta- and gamma rays, protons as well as neutrons and protons and other ionizing particles. Scintillation detectors are used in many different applications e.g., in environmental measurements, x-Ray systems, PET and SPECT scanners, computed tomography instruments, food monitors, oil logging and several spectrometers for quantitative and qualitative analysis as well as homeland security applications, especially radionuclide identifiers. Generally, the detectors may comprise a scintillation crystal, which converts the incident radiation to light pulses. The light pulses may then be detected and converted to electrical current using a photomultiplier (PMT). A PMT includes an anode and a plurality of dynodes, which may constitute a chain of dynodes. The anode and the dynodes may be connected to voltage sources which may include voltage dividers, to achieve signal amplification.
Until today, PMT signals are picked up at either electrode, at a dynode or at the anode.
Typically however, a photomultiplier is designed to deliver the output signal at the anode. The anode is the electrode where the maximum charge arrives after the multiplication stages at the dynode chain.
For further data processing, the photomultiplier output signals are digitized. Typically there are analog shaping circuits and followed by the digitization of the result. Today, sampling analog-digital converters (ADCs) are fast enough to digitize the anode or dynode currents continuously and avoid the analog shaping. The analog circuitry is replaced by digital signal processing.
Modern fast sampling ADCs, however, require differential input signals. Thus, the anode or dynode cannot be coupled directly to such ADC. Therefore, a BALUN circuit is needed. But BALUNs have certain disadvantages, apart from being just another component to be added. The amplification gain and for that matter the output current is typically high enough to drive an ADC input, so a BALUN does not have to be an active amplifier. Passive BALUNs, however have an unacceptable low frequency cutoff for photomultiplier readout applications. Active BALUNs comprise of active operational amplifiers, which add to the power budget and introduce additional noise and distortion.
Therefore, it is an object of the present invention to provide a readout circuit, PMT, and method to read out a PMT which alleviate at least partially the drawbacks of the known devices and methods as mentioned above.